Arrangement for a Die Casting Machine and Method for Operating a Drive Piston of the Die Casting Machine

ABSTRACT

The invention relates to an arrangement for a die casting machine comprising a drive piston ( 3 ) held in a working cylinder ( 2 ), wherein a piston chamber ( 4 ) is located on one side of the drive piston ( 3 ) and an annular chamber ( 5 ) is located on the other side of the drive piston ( 3 ) in said working cylinder ( 2 ), and comprising a pressure booster ( 8 ) installed upstream from the working cylinder ( 2 ), wherein a connection line ( 10, 10 ′) is used to connect the annular chamber ( 5 ) of the working cylinder ( 2 ) to the piston chamber ( 4 ) of the working cylinder ( 2 ) either directly, or via a check valve that is integrated into the pressure booster ( 8 ) or that bypasses the pressure booster ( 8 ).

The invention relates to an arrangement for a die casting machine according to the preamble of claim 1. The invention relates, furthermore, to a method for operating a drive piston in a working cylinder of a die casting machine.

Various hydraulic circuits for an injection assembly of a die casting machine became known from DE 198 42 830 A1. By means of the hydraulic circuits shown there, a drive piston received in a working cylinder can be operated. All the variants have in common that the final force of the drive piston, which is generated by the increased pressure of the pressure intensifier, is influenced as effectively as possible. The individual arrangements have the disadvantage that the pressure profile cannot be controlled in a simple way during a casting process, particularly because of the proportional valve selected there.

The object of the present invention, therefore, is to avoid the disadvantages of the known prior art and, in particular, to provide an arrangement by means of which the controllability of the pressure profile can be improved or optimized. In particular, the energy demand is also to be optimized.

This object and other objects are achieved by means of an arrangement which has the features in claim 1.

An arrangement according to the invention for a die casting machine has a drive piston received in a working cylinder and a pressure intensifier preceding the working cylinder. A piston space is arranged on one side of the drive piston and an annular space in the working cylinder is arranged on the other side of the drive piston. By means of a connecting line, the annular space of the working cylinder can be connected to the piston space of the working cylinder. In this case, this connection can be made directly or via a non-return valve. The non-return valve may be arranged so as to be integrated in the pressure intensifier or may bridge the pressure intensifier.

Since not only the annular space of the pressure intensifier is connected to the annular space of the working cylinder via a connecting line, but also the annular space of the pressure intensifier is connected to the piston space of the working cylinder via the connecting line, many different possibilities of use are afforded. Moreover, by the suitable switching of the connecting line, as shown, the quality of this influence can be appreciably increased.

A pressure medium source can be connected to said connecting line. A pressure medium can thus be fed into the hydraulic circuit in a simple way. The pressure medium source may in this case be a pump or an accumulator.

It may be especially advantageous if the arrangement has a hydraulic valve, by means of which the connecting line can be separated from the annular space of the pressure intensifier. The use of a switchable hydraulic valve arranged in the connecting line makes it possible also to employ the same connecting line for connection of the annular space of the working cylinder to the piston space of the working cylinder. The resulting differential circuit makes it possible to have an appreciable energy saving during slow movements of the working piston.

An advantageous activation of the die casting process can be achieved if a regulating valve is used instead of a simple switching valve.

Additionally or alternatively, a switching valve to the piston space of the working cylinder and/or to the piston space of the pressure intensifier may be provided in the connecting line. By means of this valve, the connecting line can be connected to or separated from the inflow side of the working cylinder or of the pressure intensifier. This switchable connection makes it possible to operate the working cylinder in a differential circuit and thus limit the pressure medium demand of the working cylinder to a minimum. The differential circuit is composed essentially of a return of the outflowing pressure medium from the annular space of the working cylinder into the piston space of the working cylinder. This return may take place directly into the piston space of a working cylinder or into the piston space of the working cylinder via the non-return valve of the pressure intensifier.

The arrangement may have at least one hydraulic valve with variable opening, with the aid of which the advancing speed of the drive piston can be influenced.

Further, the arrangement may have arranged in it a switching valve, by means of which the connecting line can hydraulically be connected to or, if required, separated from a tank.

A switching valve may then be provided, by means of which the connecting line can be connected to the pressure medium source. This switchable hydraulic connection of the connecting line to the pressure medium source makes it possible in a simple way to move the drive piston and also the pressure intensifier into the basic position again via the connecting line.

It may be advantageous, further, if the arrangement has arranged in it a hydraulic valve with variable opening which influences the advancing speed of the drive piston. This valve may be designed as a 4/3-way proportional valve.

Proportional influencing of pressure between the pressure medium source and the connecting line makes it possible to influence the annular space pressure both of the drive piston and of the pressure intensifier in an optimal way.

The invention may have two hydraulic valves which together form a hydraulic pressure divider in the connecting line. In this case, the two hydraulic valves of the pressure divider may be formed by two of the three hydraulic valves mentioned above. For example, the hydraulic pressure divider is formed by the switchable hydraulic valve, by means of which the connecting line can be connected hydraulically to the tank, and by the switchable hydraulic valve, by means of which the connecting line can be connected to the pressure medium source. Advantageously, at least one of the valves is designed as a valve with variable opening, in which case the variation in opening may take place via control signals and/or by means of direct pressure return.

A further arrangement for a die casting machine may have, independently or in combination with an embodiment mentioned above, a working cylinder and a pressure intensifier preceding the working cylinder. A drive piston is received in the working cylinder, a piston space being arranged on one side of the drive piston and an annular space in the working cylinder being arranged on the other side of the drive piston. By means of a hydraulic valve and a pressure source connected to it or by means of a hydraulic valve and an accumulator connected to it, and also by means of a hydraulic valve and a tank connected to it, a pressure divider can be formed such that a variable pressure can be fed to the connecting line between the annular space and piston space of the working cylinder.

A further aspect of the invention relates to a method for operating the drive piston in a working cylinder for an injection assembly of a die casting machine. For this method, in particular, the arrangement described above can be used. The method is distinguished in that, when the drive piston is accelerated during start-up, in a first step the hydraulic medium required for the stroke of the drive piston is obtained from a pressure medium source. Continuous run-up or smooth acceleration can thus be achieved. When, in a second step, the hydraulic medium is obtained from an accumulator, further acceleration can be achieved without the known pressure peaks arising. The acceleration of the drive piston can therefore be controlled in a simple way.

The advancing speed of the drive piston can be influenced by means of at least one hydraulic valve provided with variable opening, if the hydraulic valve is arranged in a connecting line from an annular space to a piston space of the working cylinder.

With the aid of a pressure divider, a basic volume flow from the pressure medium source via the connecting line to the tank and/or the resulting pressure in the connecting line of the pressure divider can be influenced. The quality, and, above all, dynamics of the influencing of pressure in the connecting line are thereby increased appreciably.

If the resulting pressure in the connecting line acts on the annular space of the working cylinder and/or on an annular space of a pressure intensifier preceding the working cylinder, the drive piston and piston of the pressure intensifier can be controlled especially accurately. As a result, a metal pressure acting in a casting mold can be controlled significantly more effectively.

A further aspect of the invention relates to a method for operating the drive piston in a working cylinder for an injection assembly of a die casting machine. For this method, in particular, the arrangement described above can be used. The method is distinguished in that, in a predetermined phase, a pressure medium is fed from a pressure medium source for generating a pressure on one side of the drive piston and at the same time, to generate an oppositely acting counterpressure, on the drive piston, pressure medium is also led to the other side of the drive piston, with the result that the drive piston is clamped between two oppositely acting forces. Via the connecting line which connects the two sides, that is to say the annular space of the working piston and the piston space of the working piston, to one another, in a predetermined phase in which the working piston is clamped between oppositely acting forces the pressure in the connecting line can also be conducted into the annular space of the pressure intensifier. This pressurizing of the annular space of the pressure intensifier appreciably influences the operation of the pressure intensifier.

Further features and advantages of the invention may be gathered from the following exemplary embodiments and the drawings in which:

FIG. 1 shows an arrangement according to the invention based on a modification of an embodiment according to DE 198 42 38 A1,

FIG. 2 shows a further embodiment of an arrangement, and,

FIG. 3 shows an alternative arrangement.

FIG. 1 shows an arrangement, designated as a whole by 1, for a die casting machine with a working cylinder 2 and with a pressure intensifier 8 preceding the working cylinder 2. The illustration according to FIG. 1 is based on FIG. 2 from DE 198 42 38 A1, with the most essential difference that a connecting line 10′ is arranged between the connecting lines designated by 10 and 12. Tests showed surprisingly that a switching arrangement of this type affords many different possibilities for optimization.

In FIG. 1, a casting piston 11 connected to a position measuring system 2, of a die casting machine is driven via a piston rod of a drive piston 3 which is arranged displaceably in a working cylinder 2. The movement of the working cylinder is preferably controlled via a proportional valve 14 connected to an outflow line (outflow during the injection cycle) or via signals supplied to its magnet, as is known per se and is therefore not described in detail here.

Said valve 14 may also take over the setting of the pressure in the annular space 5 of the working cylinder 2. On the outlet side of the valve 14, two lines are provided, of which one line leads directly to a pressure medium tank T, whereas the other line is connected to a pump P. Pressure-electric converters are connected to both the annular space 4 and the piston space 5. In a way known per se, the pressure intensifier 8 containing a pressure intensifier piston can be connected for an increase of pressure depending on the pressure measured by at least one of the converters. The pressure intensifier piston possesses a piston part of larger diameter and an adjoining piston part of smaller diameter which are in each case displaceable in cylinder portions. An accumulator 9 is connected in series to the pressure intensifier piston 8 and can be released or shut off via a shut-off valve 19 controlled by the signal from at least one of said pressure-electric converters.

While with the accumulator 9 released (the valve 19 illustrated in FIG. 1 is displaced to the left), the smaller piston part of the pressure intensifier 8 emits pressure to a line 12 and therefore into the piston space 4, pressure medium is displaced out of the opposite annular space 5. The pressure medium can in this case flow off into a tank T via the valve 14 only to the extent allowed by the position of the proportional valve 14. Depending on the position of the corresponding valve body, a pressure will build up in the annular space 5 of the working cylinder and counteracts the pressure in the piston space 4, so that the drive piston 3 is clamped between these opposite actions of force.

Furthermore, the pressure built up in the annular space 5 can be returned via a line 10 in order to influence the pressure intensifier piston of the pressure intensifier 8. This expediently takes place such that the line 10 connects the annular space 5 to that side (annular space 7) of the pressure intensifier piston which the smaller piston part adjoins. The line 10 may be a simple line without any costly fittings. Alternatively, however, a hydraulic valve 16 may also be incorporated in the line 10. The line 10 automatically also results in pressure regulation of the pressure intensifier by the pressure-regulating proportional valve 14 which therefore simultaneously fulfills two functions here. Clearly, in the line portion 10′ of the connecting line 10, a switching valve 17 is arranged, by means of which, if required, hydraulic coupling of the annular space 5 to the piston space 4 of the working cylinder (2) is also possible. This connection makes it possible to have an appreciable energy saving during slow stroke movements of the working cylinder (2).

FIG. 2 shows an arrangement 1 with approximately the same main components as in the first exemplary embodiment: an accumulator 9, a pressure intensifier 8 and a drive cylinder 2. By contrast, the hydraulic circuit is modified. The switchable hydraulic connection, explained in detail below, of the connecting line to the piston space 4 of the working cylinder 2 makes it possible to operate the drive piston 3 especially simply in a differential circuit, thus leading to an appreciable energy saving during relatively slow piston movements.

A pressure medium source, for example a pump, indicated by P is connected to the connecting line 10 which connects the annular space 7 of the pressure intensifier 8 to the annular space 5 of the drive piston and to the piston space 4 of the working cylinder. The arrangement 1 has a plurality of switchable hydraulic valves in the connecting line 10. By means of the switching valve 16, the connecting line 10 can be separated from the annular space 7 of the pressure intensifier 8. By means of the switching valve 17 arranged in a line portion 10′, the connecting line 10 can be separated from the piston space 4 of the drive piston. By means of the switching valve 15, the connecting line 10 can be connected hydraulically to a tank T. By means of the switching valve 18, the pressure medium source P can be separated from the connecting line. The two hydraulic valves 15 and 18 together form a hydraulic pressure divider in the connecting line 10, at least one of the hydraulic valves 15, 18 being influenced by means of a control-side or hydraulic return (not shown) of the pressure in the connecting line 10.

Theoretically, however, it is also conceivable to replace the switching valve 15-18 by hydraulic valves with variable opening or continuous valves. The use of at least one continuous valve instead of the valves 15, 17 and 18 shown in FIG. 2 makes it possible via the connecting line 10, 10′ to influence both slow and rapid movements of the drive piston 3 and the pressure in the annular space 5 of the working cylinder and in the annular space 7 of the pressure intensifier 8 especially consistently with requirements. As a result, hydraulic valves with a functionally appropriate nominal width can be used, thus greatly improving their dynamic behavior. Thus, for example, smaller and therefore faster 3-way continuous valves (instead of the valves 17 and 18 in FIG. 2) can be used, which influence the advancing speed of the drive piston 3 in a differential circuit. The larger two-way continuous valve (15) influences the rapid piston movement. The two continuous valves (15, 17) together form a pressure divider, for example a small and therefore faster valve (17) taking over pressure regulation, and the large continuous valve (15) determining the basic volume flow of this hydraulic circuit. These continuous valves (15, 17 and 18) would therefore to some extent replace the proportional valve 14 in the exemplary embodiment according to FIG. 1.

FIG. 3 shows a hydraulic circuit for an alternative arrangement. In contrast to the two preceding exemplary embodiments, the connecting line 10 is not connected directly to the piston space 4 of the working cylinder 2, but, instead, the connecting line 10, 10′ is connected to the piston space 13 of the pressure intensifier 8. This arrangement is expedient only when a non-return valve active via the pressure intensifier 8 is present. By means of this arrangement, the differential pressure at the valve 17 can be reduced considerably, so that favorable commercially available hydraulic valves can be employed. 

1-16. (canceled)
 17. An arrangement for a die casting machine with a drive piston received in a working cylinder, a piston space being arranged on one side of the drive piston and an annular space in the working cylinder being arranged on the other side of the drive piston, and with a pressure intensifier preceding the working cylinder, wherein by means of a connecting line, the annular space of the working cylinder, can be connected to the piston space of the working cylinder either directly or via a non-return valve which is arranged so as to be integrated in the pressure intensifier or which bridges the pressure intensifier.
 18. The arrangement according to claim 17, wherein a pressure medium source can be connected to the connecting line.
 19. The arrangement according to claim 18, wherein the pressure medium source is selected from the group consisting of a pump, an accumulator, or a combination of both.
 20. The arrangement according to claim 17, wherein said arrangement has a hydraulic valve, with the aid of which the connecting line can be separated from the annular space of the pressure intensifier.
 21. The arrangement according to claim 20, wherein said hydraulic valve is switchable.
 22. The arrangement according to claim 17, wherein said arrangement has a hydraulic valve, with the aid of which the connecting line can be separated from the piston space of the working cylinder or from the piston space of the pressure intensifier, or from both.
 23. The arrangement according to claim 22, wherein said hydraulic valve is switchable.
 24. The arrangement according to claim 17, wherein said arrangement has at least one hydraulic valve with variable opening, by means of which the advancing speed of the drive piston can be influenced.
 25. The arrangement according to claim 17, wherein said arrangement has a hydraulic valve, with the aid of which the connecting line can be connected hydraulically to a tank.
 26. The arrangement according to claim 24, wherein said hydraulic valve is switchable.
 27. The arrangement according to claim 24, wherein the hydraulic valve for the hydraulic connection of the tank to the connecting line is a hydraulic valve with variable opening, by means of which the advancing speed of the drive piston can be influenced.
 28. The arrangement according to claim 18, wherein said arrangement has a hydraulic valve, with the aid of which the pressure medium source can be separated from the connecting line.
 29. The arrangement according to claim 27, wherein said hydraulic valve is switchable.
 30. The arrangement according to claim 28, wherein one or more hydraulic valves have variable opening.
 31. The arrangement according to claim 30, wherein all the hydraulic valves have variable opening.
 32. An arrangement for a die casting machine with a drive piston received in a working cylinder, a piston space being arranged on one side of the drive piston and an annular space in the working cylinder being arranged on the other side of the drive piston, and with a pressure intensifier preceding the working cylinder, wherein by means of a hydraulic valve and a pressure source connected to it or by means of a hydraulic valve and an accumulator connected to it, and also by means of a hydraulic valve and a tank connected to it, a pressure divider is formed, so that a variable pressure can be fed to the connecting line.
 33. A method for operating a drive piston in a working cylinder for an injection assembly of a die casting machine, said method comprising (a) a first step of obtaining hydraulic medium from a pressure medium source when the drive piston is accelerated during start-up, (b) a second step of obtaining hydraulic medium from an accumulator.
 34. The method according to claim 33, wherein the advancing speed of the drive piston is influenced by means of at least one hydraulic valve provided with variable opening, which is arranged in a connecting line from an annular space to a piston space of the working cylinder.
 35. The method according to claim 34, wherein with the aid of a pressure divider, a basic volume flow from the pressure medium source via the connecting line to the tank, or a resulting pressure in the connecting line of the pressure divider, or both the basic volume flow and the resulting pressure are influenced.
 36. The method according to claim 34, wherein a resulting pressure in the connecting line acts on the annular space of the working cylinder or on an annular space of a pressure intensifier preceding the working cylinder, or on both.
 37. A method for operating a drive piston in a working cylinder for an injection assembly of a die casting machine, wherein simultaneously with a pressure an oppositely acting counter-pressure from a pressure medium source is also led to another side of the drive piston and wherein the pressure is variable on this side, and wherein the drive piston is thus clamped between two oppositely acting forces, the counter-pressure being derived from a pressure intensifier as a result of the hydraulic connection, wherein a connecting line connects the annular space of the working piston to the annular space of the pressure intensifier and to the piston space of the working piston. 